1. Field of the Invention
The present invention relates to an electric charging system, an electric vehicle and an electric charger, and, in particular, to a technology that checks for a failure of a relay provided to an electric vehicle.
2. Description of the Related Art
In recent years, electric vehicles that are equipped with an electric motor for propulsion have been under development. The electric vehicle is equipped with an electric storage device such as battery. Upon charging the electric storage device, a charging cable extending from an external electric charger is connected to a charging port of the electric vehicle. Furthermore, in the field of hybrid electric vehicles that are equipped with an engine and an electric motor for propulsion, so called a plug-in type vehicle is under development whose electric storage device is charged with an external electric charger. Since a terminal voltage of the electric storage device is applied to the charging port provided to the electric vehicle, it is necessary to ensure safety during a charging operation that exposes the charging port. Thus, a relay is provided to a power supply line that connects the electric storage device and the charging port. When the charging operation is not performed, the relay is disconnected, thereby protecting the terminal voltage from being applied to the charging port.
Since a large current is supplied during charging to the relay thus provided on the power supply line for ensuring safety, a weld failure or fusion failure may occur at the relay. Thus, an electric charging system is proposed that switches the relay to a disconnection state after charging is complete as well as monitors a voltage change due to the relay disconnection (see, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2010-238576). By using such an electric charging system, it is possible to detect a weld failure of the relay.
The electric charging system described in JP-A No. 2010-238576 checks for a weld failure of a relay using a voltage sensor disposed in an electric charger. Upon using a voltage output from the voltage sensor, it is necessary to perform a filtering process such as moving average to remove noise from the voltage. However, the voltage detected by the voltage sensor is used for charging control of an electric storage device in addition to for a relay failure diagnosis, it is difficult to set a filtering characteristic for processing the voltage.
Specifically, upon charging when high charging power is supplied, large noise is generated and thus a filter characteristic is required that emphasizes on stability. On the other hand, upon the relay failure diagnosis when power supply is interrupted, a filter characteristic is required that emphasizes responsiveness. Therefore, if a filtering characteristic emphasizing stability is set, it is difficult to swiftly perform the relay failure diagnosis. On the other hand, if a filtering characteristic emphasizing responsiveness is set, stability of a voltage that is filtered upon charging is impaired.